Resistance-coupled amplifier



Feb. 9, 1932. K, PQSTHUMUS 1,844,177

RESISTANCE COUPLED AMPLIFIER Filed June 6. 1927 2 Sheets-Sheet 1 INVENTOR mns POS'IHUMUS BY C fla' Adm AT RNEY Feb. 9, 1932. K. POSTHUMUS v RESISTANCE COUPLED AMPLIFIER 2 Sheets-Sheet 2 Filed June 6, 1927 INVENTOR KLASS POSTHUMUS BY r dbl 37 N rTORNEY Patented Feb. 9, 1932 uurrso STATES PATENT OFFICE KLAAS POSTHUMUS, OF EINDHOVEN, NETHERLANDS, ASSIGNOR TO RADIO CORPO- RATION OF AMERICA, A CORPORATION OF DELAWARE RESISTANCE-COUPLED AMPLIFIER Application filed June 6, 1927, Serial No. 196,725, and in the Netherlands August 16, 1926.

This invention is concerned with so-called resistance-coupled amplifiers and more particularly with those which serve to amplify especially audio-frequencies. The invention is, however, also useful if applied to the amplification of so-called medium frequencies that is frequencies of the order of magnitude of 50,000 oscillations per second.

It is known that in addition to the audiofrequency oscillations in the plate circuits of detector valves nearly always high-frequency components occur. On the low-frequency currents being amplified the said high-frequency oscillations are also submitted to amplification, especially if resistance amplifiers are used, withthe result that they may give rise to a distortion of sound. The object of the invention is to construct the resistance amplifier in such a manner that the highfrequency amplitudes, if any, will not exercise any appreciable influence on the controlling grids of the amplifying valves.

According to the invention this object is attained by so arranging the amplifier that the connecting elements (resistances and condensers) which lead to the controlling grid of one or more of the amplifying valves present to the alternating currents two partially separated paths, one of which has a practically infinite resistance to the oscillations to be amplified but gives passage to highfrequency oscillations, while the other constitutes for the high-frequency oscillations a much larger resistance but for low and medium frequency oscillations on the contrary a much lower resistance than the first mentioned path, the said controlling grid being connected to a point where the potential amplitude of the high-frequency oscillations has not only been reduced entirely or almost entirely to zero, but where the amplitude of the low and medium frequency oscillations has still remained substantially nnweakened. Preferably the circuit is so arranged that the oscillations to be amplified are led in the usual manner through a large leak resistance, and the high frequencies through an ohmic resistance having a small condenser in series with it, to a point of constant potential, the controlling grid of the amplifying valve being connected, either galvanically or through the grid condenser, to the input terminal of the leak-resistance and to the output terminal of the said ohmic resistance.

A practical form of construction according to the invention may, for example, consist in that one or more ohmic resistances are connected in series with the usual grid condenser, these ends of the said resistances which are turned to the grid being connected through small condei'isers to a point of constant potential.

The invention comprises in addition a coupling unit for use with resistance amplifiers according to the invention. The structural details of the said unit will be more clearly understood from the following description in which the invention will be set forth with reference to the accompanying drawings.

In the said drawings:

Figures 1, 2 and 3 are respectively three different circuit diagrams according to the invention.

Figures 4 and 5 are respectively an axial section and a bottom view of a construction of a coupling unit according to the invention.

Figures 6' and 7 are respectively an axial section and a plan of a modification of such a coupling unit.

Referring to Figure 1, 1 and 2 are two different resistance coupled triodes.

The plate circuit of the triode 1 includes an anode resistance 3, the plate end of which is connected through an ohmic resistance 4, in series with a grid condenser 5, to the grid 6 of the triode 2. In addition the grid 6 is connected through a leak-age-resistance 7 to a point of constant (negative) potential. The connecting point between the resistance 4 and the grid condenser 5 is connected across a small auxiliary condenser 8 to the free end of the leakage-resistance 7. The function of this device is as follows: the small auxiliary condenser-'8, which is of the order of magnitude of to centimeters, presents a practically infinitely large resistance to low and medium frequencies so that the oscillations of said frequencies make their way almost exclusively across the grid condenser'5 and the leakage resistance 7. Thus by far the greater portion of the potential drop of the said oscillations occurs in the leakage resistance 7 which must be large compared with the ohmic resistance 4, for example 10 times as large. On the contrary the hl h frequency oscillations meet with much less resistance in the condenser 8 than in the leakage resistance 7, and consequently make their way across the said condenser, the potential drop of the said oscillations taking place almost entirely within the ohmic resistance 4.

It will be seen that the grid 6, which is connected to the output terminal of the resistance 4 and to the input terminal end of the leakage resistance 7, will be little or not influenced by high-frequency potential variations, whilst but little of the low frequency and medium-frequency amplitudes is lost in the resistance 4.

The circuit arrangement shown in Figure 2 is in regard to its action exactly similar to that shown in Figure 1. However, the resistance 4 and the grid condenser 5 have been changed about, and so have the leakage resistance 7 and the small auxiliary condenser 8. Again the high-frequency oscillations make their way essentially across 48 and the low-frequency oscillations across 7.

The circuit arrangement shown in Figure 3 is similar to that shown in Figure 2 but for an additional ohmic resistance 9 and an additional auxiliary condenser 10, which ensures that high-frequency potential amplitudes which may still occur at the end of the resistance 4 will be further reduced in the resistance 9. It is evident that the circuit arrangement may be extended in this manner at will and according to circumstances.

Figures 4 and 5 show a construction of a coupling unit that permits of simply building up a circuit arrangement according to the invention. The various resistances and condensers are referred to in these two figures by like reference numerals as in Figures 1 to 3. The circuit arrangement is that according to Figure 1.

The anode resistance 3 and the resistance 4 are both so called wire resistances and are wound on an insulating case 21 that enters an insulating base 22. In said case 21 are enclosed the grid condenser 5, which is one of the spirally-wound type and the leakage resistance 7. The auxiliary condenser 8 is constituted by a metal shell 10 which obturates the top end of the case 21 and by the metal envelope 9 of the coupling unit, the distance between 9 and 10 being such that the capacity of the auxiliary condenser is about 20 to 30 centimeters. The various parts are electrically connected to the discharge tubes of the amplifier by means of connecting wires 11, 12, 13, 14, 15 and 16 and also by four studs 17, 18, 19 and 20 protruding from below the base 22, said studs being so arranged that the unit is adapted to enter thermionic valve foots of normal construction, the mounting and exchange being thus facilitated.

Figures 6 and 7 show a modified construction. The various parts are mounted on a base 23 of insulating material in which holes 30 are made by means of which it can be screwed to a base plate. The foot has fixed to it four metal studs 31 which at the bottom are connected by means of metal strips or springs 32 to four connecting terminals 29 and which carry the various resistances and condensers. The aggregate is surrounded by a metal case 27 which by means of a clamping screw 28 on the top end of a metal stem 26 can be forced against the foot. The stem 26 is secured at the bottom to a metal plate 25 which with the interposition of an insulating late 24 bears on the bottom of the foot.

he case 27 and also the plate 25 may thus be easily grounded by means of the blnding post 28, the parts of the circuit being thus prerented from influencing each other.

One of the studs 31 has mounted on it a grid condenser 33 the inner coating of which is separated from the stud 31 by an insulation of such thickness that there is between this inner coating and the said stud a capacity of 28 to 30 centimeters. This condenser is used as the auxiliary condenser, the parts being connected in circuit as shown in Figure 1.

1t will be understood that many other spec hc arrangements, associations, and connections for accomplishing the objects and purposes above set forth and for carrying my invention into practical operation, might readily suggest themselves to persons skilled in the art without departure from the spirit and scope of my invention. I therefore do not desire to be limited or restricted to any particular arrangement shown and described.

Having set forth the nature of my invention, whatI claim as new and useful and desire to protect by Letters Patent is:

1. A resistance coupled oscillation amplifier compr sing a series of triodes, means to lead oscillations from the plate of one triode to the grid of the next succeeding triode comprising two partially separate paths, one of which paths includes a large capacity and offers a high resistance to the oscillations to be amplified but which allows the passage of high frequency oscillations, the other of said paths including a lower capacity and offering a high resistance to high frequency oscillations and a low resistance to low frequency oscillations, a grid leak resistance, the said grid being connected to points of said leak resistance and said low capacity where the potential amplitude of the high frequency oscillations has already been substantially reduced but where the ampliutde of the low frequency oscillations is substantially unweakened, said leak resistance being shunted by the large capacity.

2. A resistance amplifier for low and medium frequencies including a plurality of amplifying valves, in which the connecting elements which lead to the controlling grid of one or more of the amplifying valves pro.- sent to the alternating currents two partially separated paths, one of which paths includes a high capacity and offers a practically infinitely large resistance to the oscillations to be amplified but gives passage to high-frequency oscillations, while the other path includes a low capacity in series with one or more resistances constitutes for the high frequency oscillations a much higher resistance, and for low and medium frequency oscillations a much lower resistance than the firstmentioned path, a grid leak resistance in se ries with said low capacity, the said controlling grid being connected to a point on the second path where the potential amplitude of the high-frequency oscillations has already been reduced substantially to zero but where the amplitude of the low and medium frequency oscillations has still remained substantially unweakened said leak resistance being shunted by the high capacity.

3. In combination in an amplifier including a pair of resistance coupled electron discharge tubes, a condenser between the anode of the preceding tube and the control electrode of the succeeding tube, a resistance in series with said condenser, a second condenser having a relatively smaller capacity than the first condenser connected between a point of constant potential and the end of said series resistance nearest the control electrode.

i. In combination in an amplifier including a pair of resistance coupled electron discharge tubes, a condenser between the anode of the preceding tube and the control electrode of the succeeding tube, a resistance in series with said condenser, 21. second condenser having a relatively smaller capacity than the first condenser connected between a point of constant potential and the end of said series resistance nearest the control electrode, and a leakage resistance connected to said point and said control electrode.

5. In combination in an amplifier including a pair of resistance coupled electron discharge tubes, a condenser between the anode of the preceding tube and the control electrode of the succeeding tube, a resistance in series with said condenser, a second condenser having a relatively smaller capacity than the first condenser connected between a point of constant potential and a point between said series resistance and said first condenser, and a leakage resistance connected to said con stant potential point and said control electrode.

6. A resistance coupling unit for tube amplifier circuits, comprising a base provided with a plurality of spaced terminals, a metallic casing disposed upon said base and adapted to be connected to a point of constant po tential, a coupling resistance disposed within said casing, a second resistance in series with a grid condenser connected to said coupling resistance disposed within said casing, a leakage resistance disposed within said casing and having a condenser of relatively small capacity shunted across it, all of said members within said casing being connected to said terminals.

7. A resistance coupling unit for tube amplifier circuits comprising a base provided with a plurality of spaced terminals, a metallic casing disposed upon said base and adapted to be connected to a point of constant potential, a coupling resistance disposed within said casing, a second resistance in series with a grid condenser connected to said coupling resistance disposed within said cas1ng,aleakage resistance disposed within said casing and having a relatively small capacity shunted across it, all of said members within said casing being connected to said terminals, said metallic casing comprising one of the electrodes of said condenser of relatively small capacity.

8. A resistance coupling unit for tube amplifier circuits, comprising an insulating base provided with a plurality of spaced metallic terminals, a metallic casing disposed upon said base and adapted to be connected to a point of constant potential, a coupling resistance disposed within said casing, a second resistance in series with a grid condenser connected to said coupling resistance disposed within said casing, a leakage resistance disposed within said casing and having a relatively small capacity shunted across it, all of said members within said casing being connected to said terminals, said metallic casing comprising one of the electrodes of said condenser of relatively small capacity.

9. In combination in an amplifier including a pair of resistance coupled electron discharge tubes, a condenser between the anode of the preceding tube and the control electrode of the succeeding tube, a resistance in series with said condenser, a second condenser having a relatively smaller capacity than the first condenser connected between a point of constant potential and the end of said series resistance nearest the control electrode, the first condenser being connected bctween the anode and the end of the series resistance furthest from the said control electrode.

10. In combination in an amplifier including a pair of resistance coupled electron discharge tubes, a condenser between the anode of the preceding tube and the control electrode of the succeeding tube, a resistance in series with said condenser, a second condenser having a relatively smaller capacity than the first condenser connected between a point of constant potential and the end of said series resistance nearest the control electrode and a resistor connected between said point and a point between said first condenser and the series resistance.

11. In combination in an amplifier including a pair of resistance coupled electron discharge tubes, a condenser between the anode of the preceding tube and the control electrode of the succeeding tube, a resistance in series with said condenser, a second condenser having a relatively smaller capacity than the first condenser connected between a point of constant potential and the end of said series resistance nearest the control electrode and a third condenser connected in shunt with the second condenser.

12. In combination in an am lifier including a pair of resistance couple electron discharge tubes, a condenser between the anode of the receding tube and the control electrode o the succeeding tube, a resistance in series with said condenser, a second condenser having a relatively smaller capacity than the first condenser connected between a point of constant potential and the end of said series resistance nearest the control electrode, a third condenser in shunt with the second condenser, and a-resistor connected in shunt with said second and third condensers.

' KLAAS POSTHUMUS. 

